IN CEYLON. 37 



forest the xylem is characterized by large radial strands, 

 0*09 mm. in tangential width, of very large parenchyma. 

 These often commence at the pith and run inwards for a 

 distance of several millimetres ; they die out gradually, but 

 frequently at the pointed end another radial patch commences 

 and extends a considerable distance into the younger 

 secondary xylem. 



Similar strands occur in D. Gardneri from Peradeniya, the 

 component cells being about twice the size of ordinary 

 parenchyma and surrounded by fibres or flanked by a 

 medullary ray. When more than one cell broad the cells are 

 usually irregularly disposed, occasionally they exhibit a 

 radial arrangement, though in no cases do the components 

 exhibit the radial regularity of other elements of the 

 secondary xylem. 



The cells are parenchymatous with transverse dimensions 

 often equal to those of the neighbouring vessels ; they 

 possess thin walls, and their contents include starch and 

 oxalate of lime. These strands may be purely pathological, or 

 they may perform some part in the physiology of a secondary 

 xylem of such slow rate of growth. They cannot be 

 regarded as parenchyma drawn from the peri medullary 

 zone, because they appear in the sap wood of old trees ; their 

 presence in radial groups suggests an origin from the 

 cambium similar to the broad medullary rays, and accepting 

 this as the interpretation one must regard the final irregular 

 disposition of the component cells as a consequence of 

 active growth evidenced in their abnormal dimensions and 

 numerous contents. 



The Percentage Composition of the Secondary 

 Xylem. 



These calculations have been arrived at by examination 

 of transverse sections of the secondary xylem of young 

 twigs and the sapwood of old trees. The number of 

 elements of each type within a fixed field of view have been 

 counted, and after several ureas have been so examined for 



291989 



